This invention relates to fastening devices, implants and articles used in surgical procedures.
Surgical fasteners such as staples, clips, clamps, bands, tacks, or other wound or incision closure devices are commonly used in surgical procedures to allow a surgeon to fasten, secure and/or repair body tissue quickly without the need for time consuming suturing. Examples of surgical fasteners are given in U.S. Pat. Nos. 4,994,073 or 4,950,284 or 4,934,364, or 4,932,960.
Surgical fasteners are designed to be inserted into and to join tissue or layers of tissue. In so doing, they are adapted to receive a mechanical load or stress without substantial deformation or breakage. The stress may be generated at different points in time and may arise from different stimuli. For example, when the fastener is a two-part device, such as that shown in U.S. Pat. No. 4,932,960, a generally U-shaped fastener member is ejected from a stapling device, passed through tissue, and lodged into a retainer member. Consequently, the backspan of the U-shaped fastener member receives a load when the pusher of the stapling device contacts the backspan and propels the fastener out of the device. The fastener member also receives loads when its prongs penetrate the tissue, and further, when the prongs contact and mate with the retainer. In order to function properly, the fastener and retainer should be designed and constructed to withstand operational stress without substantial deformation or breakage. Once in place, the fastener must also withstand the shearing stress placed upon the tissue, and consequently, on the fastener itself, which is created by the characteristics of tissue interaction in a living creature.
The ability of a fastener to withstand stress is determined by the kind of material, the amount of material, and the shape of the fastener's various structural members. It is desirable to optimize these variables, generally by providing the greatest strength to mass of material ratio so as to minimize the amount of foreign material in the body.
The structural members of surgical fasteners commonly have a solid circular, ellipsoidal, rectangular or polygonal aspect. The flex and bend strengths of such members are usually more than sufficient to withstand the loads required in surgical applications, e.g., firing the parts into tissue or during the holding period during which healing occurs and tissue strength is increasing.
Surgical fastening devices may be designed with open grooves or channels to guide the fastener component of a two-piece surgical fastening device from the stapler into a retainer component, see, for example U.S. Pat. No. 4,513,746. The retainer component receives the legs of the fastener component through tubular columns that become substantially completely filled by the legs of the fastener component. Other exteriorly disposed open grooves pertaining to surgical hemostatic clips are disclosed in U.S. Pat. Nos. 4,976,722 or 4,702,247. Such exterior grooves are designed to help grab and secure a blood vessel or artery. U.S. Pat. No. 3,918,455 discloses a hollow filament suture designed to receive and secure the shank of a suture needle. The hollow core of the suture is designed to collapse under stress. The collapsable nature of the core improves knotability through compressibility of the hollow filament under the tension of knotting.
Various materials are used in the manufacture of surgical fasteners and implants. These materials must be biocompatible, i.e., they do not adversely affect the surrounding living environment, and conversely, their performance is not adversely affected by the surrounding living environment. The materials may be inert non-absorbable or biodegradable. Inert materials may be fairly indestructible and maintain their form and function for extended periods of time.
Biodegradable materials are intended to break down and dissolve during and after the healing process. Biodegradation may occur, e.g., by hydrolysis as in the case of certain ester compounds or by enzymatic degradation as in the case of certain proteins. The time it takes for biodegradable fasteners to dissolve depends, inter alia, upon the inherent solubility of the material, the amount of the material present, the density of the material, and the amount of contact with bodily fluids that decompose the material. Optimally, a biodegradable fastener maintains its structural integrity in situ long enough for the tissue being fastened to gain sufficient strength to be self-supporting.
In general, a well-designed surgical fastener or implant should minimize the amount of material needed to create optimum structural integrity. Non-efficient use of materials wastes expensive resources and results in implants or fasteners that are heavier than necessary. Creating lighter implants or fasteners is desirable because less stress would be placed on the surrounding tissue system than might normally result from fasteners of excess mass. Moreover, in the case of biodegradable materials, the ability to exert greater control over adjustments in the density and amount of material used would permit greater regulation of the time it takes for the implant or fastener to be dissolved and absorbed into the living system. Indeed, once the fastened tissue is capable of suitable self-support, it is advantageous for the biodegradable material to be dissolved as quickly as possible to reduce continuing tissue interaction with the material.
Consequently, the need to optimize the strength to mass ratio of surgical implants and fasteners is clear. The present invention optimizes the mass to strength ratio in the creation of structurally sound surgical implants and fasteners.